There are two frame structures in the Long Term Evolution (LTE) system, a frame structure Type 1 is applicable to Frequency Division Duplex (FDD) and frequency division half-duplex. The length of each radio frame is 10 ms and composed of 20 slots, each slot is 0.5 ms and numbered from 0 to 19. Wherein, one subframe is composed of two successive slots, for example, a subframe i is composed of two successive slots 2i and 2i+1.
A frame structure Type 2 is applicable to Time Division Duplex (TDD). The length of one radio frame is 10 ms and composed of two half-frames with lengths of 5 ms. One half-frame is composed of five subframes with lengths of 1 ms. A particular subframe is composed of a downlink particular subframe (DwPTS), a Guard Period (GP) and an uplink particular subframe (UpPTS), whose total length is 1 ms. Each subframe is composed of two slots 2i and 2i+1 with lengths of 0.5 ms (15360×Ts).
In the above two frame structures, with regard to a Normal Cyclic Prefix (Normal CP), one slot contains 7 symbols with lengths of 66.7 microsecond (us), wherein a CP length of the first symbol is 5.21 us, and a length of each of the rest 6 symbols is 4.69 us; with regard to an Extended Cyclic Prefix (Extended CP), one slot contains 6 symbols, and a CP length of each symbol is 16.67 us.
One Resource Element (RE) is an Orthogonal Frequency Division Multiplexing (OFDM) symbol in a time domain and a subcarrier in a frequency domain; one slot contains NsymbDL OFDM symbols, one Resource Block (RB) consists of NsymbDL×NscRB resource elements, and it is one slot in the time domain and 180 kHz in the frequency domain; when the cyclic prefix of the subframe is the normal cyclic prefix, one resource block is as shown in FIG. 1; and it corresponds to a RB-pair in the same frequency domain in one subframe.
The following three kinds of downlink physical control channels are defined in the LTE: a Physical downlink Control Format Indicator Channel (PCFICH), a Physical Hybrid Automatic Retransmission Request Indicator Channel (PHICH) and a Physical Downlink Control Channel (PDCCH). Wherein, information borne on the physical downlink control format indicator channel indicates a size of the time domain of the downlink control area in the subframe.
The physical downlink control channel PDCCH is mapped to physical resources in a unit of Control Channel Element (CCE), a size of one CCE is 9 Resource Element Groups (REG) namely 36 resource elements, one PDCCH has four kinds of Aggregation Levels, the four kinds of aggregation levels respectively correspond to one PDCCH occupying 1, 2, 4 or 8 CCEs, called an aggregation level 1, an aggregation level 2, an aggregation level 4 and an aggregation level 8, corresponding to the four formats of the PDCCH, that is, the aggregation level represents the size of the physical resource occupied by the physical downlink control channel. Moreover, search space of the physical downlink control channel of the user equipment is divided into common search space and user equipment-specific search space, wherein, the number of location candidates corresponding to each aggregation level (1, 2, 4, 8) in the user equipment-specific search space is 6, 6, 2, 2 respectively.
In the kth subframe, a control domain bearing the PDCCH is constituted of a group of NCCE,k CCEs numbered from 0 to NCCE,k−1. The UE should detect a group of PDCCH candidates in every non-Discontinuous Reception (non-DRX) subframe to acquire control information, the detection refers to decoding the PDCCHs within the group according to all DCI formats to be detected. The PDCCH candidates required to be detected are defined by means of the search space, and with regard to the aggregation level Lε{1, 2, 4, 8}, the search space Sk(L) is defined by a group of PDCCH candidates. A CCE corresponding to a PDCCH candidate m in the search space Sk(L) is defined by the following formula:L·{(Yk+m)mod └NCCe,k/L┘}+i,
wherein i=0, . . . , L−1, m=0, . . . , M(L)−1, M(L) is the number of PDCCH candidates to be detected in the search space Sk(L).
With regard to the common search space, Yk=0, L is 4 and 8.
With regard to the UE-specific search space, L is 1, 2, 4 and 8.Yk=(A·Yk−1)mod D, 
wherein Y−1=nRNTI≠0, A=39827, D=65537, k=└ns/2┘, └ ┘ represents rounded down, ns is a slot number in one radio frame. nRNTI is a corresponding Radio Network Temporary Identifier (RNTI).
In the Release (R) 8/9 of the LTE system, in order to measure the quality of the channel and demodulate the received data symbol, a Common Reference Signal (CRS) is designed. The User Equipment (UE) can perform measurement of the channel through the CRS, thereby supporting the UE to perform cell reselection and handover to a target cell. In the LTE R10, in order to improve a cell average spectrum utilization ratio, a cell edge spectrum utilization ratio and a throughput rate of each UE, two kinds of reference signals are respectively defined: a Channel State Information-Reference Signal (CSI-RS) and a Demodulation Reference Signal (DMRS), wherein, the CSI-RS is used for the measurement of the channel, the DMRS is used for the demodulation of the downlink shared channel, through the DMRS demodulation, interference between different receiving sides and different cells can be reduced with the method of beam, and performance reduction caused by the codebook granularity can be decreased, and overhead of the downlink control signaling is also reduced to a certain extent.
In a heterogeneous network, since different base station types have stronger interference, in consideration of an interference problem of a Macro eNodeB to a Pico eNodeB and an interference problem of a Home eNodeB to the Macro eNodeB, the LTE R11 proposes to solve the interference problems with a multi-antenna transmission method based on the user-specific pilot frequency, moreover, by mapping the PDCCH to a PDSCH area, and by means of frequency division multiplexing similar to PDSCH multiplexing, frequency domain coordination of the inter-cell interference can be implemented. Such enhanced PDCCH is called ePDCCH (enhanced PDCCH).
With respect to transmitting and receiving of the ePDCCH, no effective solution has been proposed at present.